XML 601 R121.htm IDEA: XBRL DOCUMENT v3.20.4
Taxation - Summary of tax relating to components of other comprehensive income or loss (Footnotes) (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Income tax relating to components of other comprehensive income that will be reclassified to profit or loss [abstract]      
Deferred tax credit (charge) included in other comprehensive income $ 115,000,000 $ 77,000,000 $ (325,000,000)
Current tax charge included in other comprehensive income $ 0 $ 0 $ 0